1. Technical Field
The subject matter described here generally relates to fluid reaction surfaces with specific blade structures that are formed with a main spar, and, more particularly, to wind turbine blades having molded shear webs.
2. Related Art
A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy. If the mechanical energy is used directly by the machinery, such as to pump water or to grind wheat, then the wind turbine may be referred to as a windmill. Similarly, if the mechanical energy is converted to electricity, then the machine may also be referred to as a wind generator or wind power plant.
Wind turbines are typically categorized according to the vertical or horizontal axis about which the blades rotate. One so-called horizontal-axis wind generator is schematically illustrated in FIG. 1 and available from General Electric Company. This particular configuration for a wind turbine 2 includes a tower 4 supporting a nacelle 6 enclosing a drive train 8. The blades 10 are arranged on a hub to form a “rotor” at one end of the drive train 8 outside of the nacelle 6. The rotating blades 10 drive a gearbox 12 connected to an electrical generator 14 at the other end of the drive train 8 arranged inside the nacelle 6 along with a control system 16 that receives input from an anemometer 18.
The blades 10 generate lift and capture momentum from moving air that is them imparted to a rotor as the blades spin in the “rotor plane.” Each blade is typically secured at its “root” end, and then “spans” radially “outboard” to a free, “tip” end. The distance from the tip to the root, at the opposite end of the blade, is called the “span.” The front, or “leading edge,” of the blade connects the forward-most points of the blade that first contact the air. The rear, or “trailing edge,” of the blade is where airflow that has been separated by the leading edge rejoins after passing over the suction and pressure surfaces of the blade.
As illustrated in FIG. 2, the blades 10 for such wind turbines 2 are typically fabricated by securing various “shell” and/or “rib” portions to one or more “spar” members extending spanwise along the inside of the blade for carrying most of the weight and aerodynamic forces on the blade. The spars are typically configured as I-shaped beams having a web, referred to as a “shear web” 20, extending between two flanges, referred to as “caps” or “spar caps,” that are secured to the inside of the suction and pressure surfaces of the blade. However, other shear web configurations may also be used including, but not limited to “C-,” “L-,” “T-,” “X-,” “K-.” and/or box-shaped beams, and the shear webs 20 may also be utilized without caps. For example, U.S. Pat. No. 4,295,790 discloses a blade structure for use in a windmill with metal shear webs and subassemblies that are filled with approximately two pound cubic foot density rigid urethane foam.
Other conventional shear webs typically consist of a foam core that is coated by a resin-infused composite material. The core is typically formed from multiple foam sheets that are connected with adhesive and then trimmed to form the desired shape of the shear webs 20. These connected foam sheets inside of the shear web then act as a spacer for the composite material coatings on either side but do not provide much additional structural benefit to the shear web 20.